The present invention relates, in general, to semiconductor processing, and in particular, to methods for doping strained heterojunction semiconductor devices.
Strained heterojunction semiconductor structures including silicon/silicon-germanium (Si/Si.sub.1-x Ge.sub.x) devices have been reported. These structures are used to form devices such as heterojunction bipolar transistor (HBT) devices or enhanced mobility metal-oxide semiconductor field effect transistor (MOSFET) devices. Strained heterojunction semiconductor structures are very attractive for high performance electronic devices and circuits because they provide a silicon-based technology with enhanced carrier mobility compared to pure silicon. Also, silicon-based strained heterojunction devices are more cost effective than III-V based heterojunction devices making them more preferable in certain applications.
When ion implantation is used in the fabrication of strained heterojunction devices, high concentrations of implantation-induced point defects and point defect clusters are known to substantially enhance the relaxation of the strained semiconductor lattice. This relaxation destroys, among other things, the enhanced carrier mobility effect. Also, ion implantation related damage can lead to the formation of dislocation and dislocation loop defects in subsequent high temperature processes. These defects can detrimentally affect the electrical characteristics of the strained heterojunction device, which in turn affects device manufacturing yield and reliability. In addition, unless the process used to activate the implanted dopants is done under appropriate conditions, it is difficult to both activate the implanted dopants and anneal the implant related damage while at the same time maintaining the strained heterojunction in a strained condition.
As is readily apparent, a need exists for a method of doping strained heterojunction devices with ion implantation that reduces implant related damage, that results in a device having good electrical characteristics, that effectively activates the implant dopants, and that minimizes relaxation of the strained heterojunction.